Testing device and method for signal light reflectors



y 4, 1935. K. w, ABENDROTH 2,001,660

TESTING DEVICE AND METHOD FOR SIGNAL LIGHT REFLECTORS Filed July 31, 1931 7t wlNVEgTOR BY MM mm,

fl Anonusv Patented May 14, 1 935 UNITED STATES PATENT OFFICE-- TESTING DEVICE AND METHOD FOR/SIGNAL LIGHT nEFLEc'roas Karl W. Abendroth, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application July 31, 1931 Serial No. 554,272 I 7 Claims. (01. 8814) This invention relates to a means and method for testing the contours of reflectors and for 10- catingthe focal points thereof. It more particularly relates to a means and method for checking the contour of a commercial ellipsoidal reflector against predetermined toleration limits of error and for locating a lamp filament at the focal point of such reflector.

A perfect ellipse has two foci or points so located that the sum of the distances from each of these points to any one point on the ellipse is constant. Also, if a point source of light beplaced exactly atone focus of a semi-ellipsoidal reflector, the rays of light reflected therefrom converge at the other focus of the completed ellipsoid.

For railway signal purposes certain color light signals are used which employ such a semir-ellipsoidal reflector to concentrate the light from an incandescent lamp, placed with its filament substantially at one focus, through a small colored roundel placed substantially at the conjugate focal point of the ellipsoidal reflector, which point is also the principal focus of a projection lens train placed ahead'of the reflector. In the commercial production of such reflectors, certain imperfections occur in the ellipsoidal contour which may sufficiently distort the focus of the reflected rays as to materially reduce the effectiveness of the signal.

Unless precision filament lamps are used in such reflectors, it is found that the position of the filament relative to the base varies sufficiently to necessitate individual adjustments of their sockets relative to the reflector in order to locate their. filament sufflciently near the focal point. This adjustment, when replacing lamps in signals which are in service, particularly in the field, is arather difficult task because of the inconvenience of determining-exactly when correct adjustment has been made. I v j In view of the above facts, it is proposed, in accordance with this invention, to provide a device whereby the contour of a reflector can be checked by projecting reflected light beams from a plurality of points on the reflector and checking the focus of the same on a predetermined focal point. I v

It is also proposed, as a modification of this invention, to provide a device whereby the loca-. tion of a lamp filament with respect to a reflector can be determined, tov facilitate in establishing such a lamp filament at thejfocalpoint of the reflector.

tures of the present invention will appear as the these apertures 3 and the number of rows thereof Other objects, purposes'.and characteristic .fea-

description thereof progresses, during which references will be made to the accompanying drawing which shows, solely by the way of example, and in no manner in a limiting sense, one form which the invention can assume, and in whichw- Fig. 1 is a sectional view of one embodiment of the'present invention shown assembled on a reflector unit.

Fig. 2 is Fig. 1.

Fig. 3 is an enlargedview of a focusing target which is a part of the device shown in Fig. 1.

Fig. 4 is a view of a modified device according to the present invention. Fig. 5 is a front View of the device shown in Fig. 4. v

The device-proposed for testing reflector con tours is illustrated in Figs. 1 and 2 and consists primarily of a casing C which is adapted to receive' thereflector unit to be tested as shown in dashed lines in the sectional view of Fig. 1. The reflector unit shown is, for example, of the type included in the application of O. S. Field, Ser. No. 470,056 dated July 23, 1930 and consists essen-, tiallyof a suitable semi-ellipsoidal reflector R held in'a cup I which adjustably holds a socket 2, containing an incandescent lampL. The socket 2 is so mounted 'as to be adjustable in any plane relative to the reflector which permits a very accurate location of the filament of the lamp L."

The casing ,C has retaining clips (not shown), similar to, the ones employed to hold the cup I. in its signal'unit, whereby the cup I is-definitely held in the casing ,C so that the front of the re flector R is covered'by a flat circular end C of the casing C. The end Clhas four radially'spaced rows of small lightftransmitting apertures 3,' whichrows, in the'form shown are substantially spaced in quadrature relation. The spacing of a front view of the device shown in displaced from the adjacent ones, so thatat' one position of the disc D only four of the apertures 5, aline with four of the apertures 3 of the casingca It is therefore evident that at a successionof dif-[i' ferent angular rotating positions of the disc D, a.

succession of apertures in the end C of accord-" ingly varying distances from the center are alined with apertures in the disc D- The dotted lines in Fig. l projecting from the filament of the lamp L represent light beams given off by the lamp filament and passing through the alined apertures previously described.

These rays which pass through apertures alined at different distances from the center of the discs are reflected from points located at proportional distances from the center of the reflector R.

The casing C has an extending upturned arm C into which is threaded a screw 6 having a smooth fiat surface facing the disc D with its center point located at the second focus of the ellipsoid of which the reflector R is a part. This screw 6 may be suitably called a focusing target and may include rings radially graduated on its surface, such as shown in the enlarged view in Fig. 3.

Considering now that the reflector being tested has a perfectsemi-ellipsoidal contour, an energization of the filament of the lamp L will produce light beams which will be directed by the reflector R through apertures, alined inany angular position of the scanning disc D, upon the focusing target 6. These light beams form four images of the filament at the center of the target 6. However, if deviations from a perfect contour occur, the beams reflected from the imperfect portion of the reflector R will not strike the center of the target 6 and from theposition of the scanning disc D it will be possible to determine in what part of the reflector the imperfections occur.

In as much as these light beams are concentrated to form an apparent source at the principal focus of a projection lens train, as is clearly disclosed in the above mentioned application, the degree of imperfection which may be tolerated dependson the permissible divergents of the final beam and this toleration limit may be conveniently placed on the target 6 in the form of rings as shown in Fig. 3. v a

The modified form shown in Figs. 4 and 5 is a device for determining the proper location of a filament of a lamp with respect to its reflector rather than for testing a reflector in which the filament has been pre-located in the focal point, as is the case in the instrument shown in Figs. 1, 2 and 3, except that the scanning disc D is omitted and only four apertures 3'are included rather than the four rows of apertures as in the other device. These four apertures may be located anywhere in the circular'end C but it is preferable to locate them at such a distance from the center of the circular end C that they will emit the rays reflected from the most effective part of the reflector R.

I In using the above described instrument to replace a lamp, the reflector unit is removed from the signal and inserted in the casing C where the filament of the new lamp is energized. The lamp socket is now moved in line with the focal axis by the adjustment therefor until four images of the filament converge at a point somewhere on the, face of the focusing target 6. An adjustment of the lamp socket is next made by the adjustments for moving in a plane at right angles to the focal axis, until the converging filament images appear at the target 6. 1

When the filament has thus been properly located the adjustment means may be securely fixed, and the reflector unit replaced in its signal with the assurance that the signal light is proper- 1y positioned for maximum intensity. I

exact center of the focusing It will now be seen that a device has been provided which is adapted to test the contour of reflectors by selecting a plurality of points on its surface and checking the uniformity of the position focal point of light rays reflected therefrom. It is proposed to use such an instrument to produce and select uniform and correctly shaped reflectors, and to use a modification of this invention to determine the proper lamp filament location in such a. reflector.

' In as much as the contours of these reflectors have been previously checked by the first instrument, the focal point of a light ray reflected from any one point on the reflector may be considered as typical of reflected rays from all points thereon. Consequently it is considered sufiicient to employ only a few light apertures, say four, spaced as shown in Fig. 5, to locate the filament,

' as a very distinct focal point can be thus obtained.

It may be found more convenient to employ a different type of focusing target than the screw 6, such as a ground glass roundel held in a ring in the upturned arm 0 so that the filament images may be viewed from thefront or back of the glass roundel. 1

The above rather specific description of one form of the present invention isgiven solely by the way of example, and is not intended, in any manner whatsoever, in a limiting sense. It is also to be understood that various modifications, adaptations and alterations maybe applied to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention, except as limited by the appended claims. 7

Having thus shown and described my invention, what.Ic1aimis:,- V

1. In testing means forelliptical reflectors, in combination, a casing, means in the casing for receiving in elliptical reflector in a predetermined'position therein and a light source at the principal focus of the reflector, a target positioned at the conjugate focus of the reflector, and a fixed disc having a plurality of minute apertures therein positioned between the light source and the target and a movable discmovably-positioned over the fixed disc and having apertures'therem which can be selectively alined with the apertures in the fixed disc upon movement of the movable disc, said'flxed disc being opaque, and having its apertures radially spaced, said movable discheini opaque and rotatably mounted on the fixed disc and having its apertures radially and singularly spaced therein, whereby. to completely scan. the

surface of the reflector with respect to. light'rays' passing from, the reflector to the target.

2. In a testing device for ellipticalrefleotors. in combination; .means "for holding a reflector in fixed position, means for holding a p nt light source at the theoretical principal focus of the reflector, a target having a light receiving surface positioned at the theoretical conjugate focus. of the reflector, and an opaque screen, with a 'plurality of minute lishttransmitting portionstherein, positioned between the'light'source and the target, whereby light passing through the. several transmitting portions of the screen will form. a singl point of lighten thejtargetomy if the reflector under testv be substantially perfect, and means for selectively covering various of the transmitting portions ofthe screen, whereby to. explore the surface of the reflector. i

3. A test fitting. including a. casing to'reaeive and hold in fixed position, an elliptical reflector and a light source at the principal focus of the reflector, a light receiving surface at the conjugate focus of the reflector, a fixed disc of opaque material positioned between the light source and said surface, said disc covering substantiallythe entire area of the reflector and having minute apertures therein distributed over its area, and means for selectively leaving only various groups of said apertures uncovered.

4. In a testing means for elliptical reflectors, in combination, an open ended receiving casing, the opening in the end of the casing being of a shape to snugly receive always in the same invariable position a light source and elliptical reflector carrying casing with the light source at the principal focus of the reflector, a target carried by the casing and positioned at the conjugate focus of the reflector, and a fixed disc having a large number of minute apertures therein positioned between the light source and the target.

5. In a testing means for elliptical reflectors, in combination, an open ended receiving casing, the opening in the end of the casing being of a shape to snugly receive always in the same invariable position a light source and elliptical reflector carrying casing with the light source at the principal focus of the refiector,a target carried by the casing and positioned at the conjugate focus of the reflector, and a fixed disc substantially covering the area of the reflector and having a plurality of minute apertures therein distributed over the area of the disc, the disc being positioned between the light source and the target, and a disc movable over the fixed disc and having apertures therein which can be caused to selectively register with the apertures in the fixed disc in a predetermined manner, whereby to allow light beams reflected from various points on the reflector to pass through the discs to the target.

6. A method for testing elliptical reflectors, comprising, placing a light source at the theoretical principal focus of a reflector to be tested, placing a receiving target, at the theoretical conjugate focus of the reflector, and progressively exploring scattered points over the entire reflecting surface of the reflector, by successively allowing only the light reflected from groups of spaced points on the reflector to reach the target.

'7. A method for testing elliptical reflectors, comprising, placing alight source at the theoretical principal focus of a reflector to be tested, placing a receiving target at the theoretical conjugate focus of the reflector, and progressively exploring scattered points over the entire reflecting surface of the reflector, by successively allowing only the light reflected from a plurality of points on the reflector to reach the target.

KARL W. ABENDROTH. 

